My cousin has a match of 279cM with a person who also matches me with 112cM. My cousin (of course) is high on my own list of over 10000 unfiltered matches. Yet when I choose this 3rd person who clearly matches both of us and select "in common with" my cousin's name does not appear. In fact only one other person comes up as a common match. Why is my cousin not on the "in common with" list?

Are you matching on the same chromosomes. Or is it possibly that you are carrying one section of the family DNA and your cousin is carrying another section. You have enough of the DNA for your cousin to match you, but not to match another person.

I'm not sure how to explain what I mean except to give an example. My brother and I are full siblings, but at a certain point our DNA is different enough that we don't have matching lists of cousins. About 50% of each of our match lists don't match the other sibling. My brother has a longer list of matches than I do as well.

Thanks ech124! That is the explanation. When I clear the name box after selecting the person and then wait long enough for the match list to regenerate, if I then choose "in common with" my list of matches drops from about 11000 to about 3000 (including my cousin). It would be nice if there was a simple set of instructions for using "in common with" somewhere that indicated this step was necessary. Thanks again!

I just had a 3rd cousin (A) ask me much the same question. He matches both my brother and I, and has found a 2nd cousin (B) who matches him and my brother, but I don't come up as in common with his 2nd cousin.

(B) is coming up a distant cousin to my brother as they only share about 25cM. Those 25 cMs are not ones that I carry, as not enough of the DNA line has past to me to be called a match by FTDNA.

When I do an in common with test using my brother's results, I can click on (A) who we both match and ask for the filter to give me all of the in common with my brother and him. His second cousin (B) pops up. As do about 97 other people including me.

But if I try an in common with (B), and my brother, I'll get (A)on the list, but I'm not. And there are only 64 matches in common with (B) and my brother, as they are sharing a much smaller amount of DNA.

So depending how you look at and filter the in common with comparisons might be why you think the filter is in error.